Carbon dioxide assimilation is increased in A. suecica over progenitor levels, particularly at higher light levels. Progenitor and allopolyploid plants were grown for 21 to 25 d in the greenhouse in individual pots (“Conetainers”). For CO₂ assimilation measurements, pots with plants were inserted into the Arabidopsis RGB cuvette of the LI-COR 6400 gas analyzer and acclimated at 1,000 µmol m⁻² s⁻¹ for 20 min. Light response curves were then measured using an automated function of the LI-COR 6400 starting with a photon flux density of 2,000 µmol m⁻² s⁻¹ and dropping incrementally lower in 2-min intervals. Data were statistically analyzed for each light level individually using a Kruskal-Wallis test coupled with a subsequent Nemenyi test for pairwise analysis. Black triangles, A. suecica (AS); blue diamonds, A. thaliana (AT); red crosses, A. arenosa (AA). The nine letters above the graph indicate which species are statistically significantly different from each other at each of the nine different light levels (P < 0.05). A, no differences between any of the species; B, AS different from both AA and AT, but AA = AT; C, AA different from AS and from AT, but AS = AT; D, all three species different from each other. Data were measured at the following light levels: 0, 20, 50, 100, 200, 500, 1,000, 1,500, and 2,000 µmol m⁻² s⁻¹. Data points are “jittered” to avoid excessive overlay of data points. Sample sizes: AS = 32, AT = 24, and AA = 22. The entire experiment was done twice separately with similar results and data were combined. Both respiration and photosynthetic rates are enhanced in the allopolyploid over the progenitors at the extreme ends of the light level spectrum.